This invention relates to calendar calculating devices and in particular to such devices which aid a female user to ascertain the days of fertility in her present menstrual cycle.
It is well known that a female is susceptible to impregnation during only a portion of her menstrual cycle. Specifically, the normal female is capable of being impregnated by sexual intercourse only when such intercourse occurs during that portion of the menstrual cycle that is near in time to ovulation.
It has been found that ovulation occurs between the fourteenth to sixteenth day prior to the beginning of the female's next menstrual cycle. This is true even for females having menstrual cycles which are irregular in length. Further, it is known that the life expectancy of an ovum is approximately one day and the life expectancy of the male sperm is approximately two days. Therefore, after allowing a day before and two days after ovulation, a female is fertile or capable of being impregnated during a period extending from the eleventh to the nineteenth day prior to the beginning of her next menstrual cycle. By knowing when a present menstrual cycle of a female is to end, it is possible to ascertain the days of fertility during the menstrual cycle. A problem occurs in that, although a normal menstrual cycle is reckoned to be a constant twenty-eight days, many females have a regular menstrual cycle of a constant length other than twenty-eight days and still others have menstrual cycles of irregular length; for example, a certain cycle of a woman may be twenty-four days whereas the next cycle may be thirty-two days.
Prior examples of such calculating devices for the woman to utilize herself have proven to be ineffective or unacceptable for various reasons. Some of the prior devices have not had the capability of enabling females who have menstrual cycles which are not a constant twenty-eight days in length to predict or ascertain their potential period of fertility. Still other examples of the prior art have been cumbersome and complicated to understand thereby decreasing their effectiveness to a user. In addition, prior art devices normally fail to function if a user's period is irregular in nature.